The Nexplanon hormonal implant is for long-lasting birth control. Free birth control has been linked to a decrease in teen pregnancies. / Merck via AP

by Kim Painter, Special for USA TODAY

by Kim Painter, Special for USA TODAY

An experimental project that gave free birth control to more than 9,000 teen girls and women in one metropolitan area resulted in a dramatic decrease in abortions and teen pregnancies, a new study shows.

It wasn't just the "free" part that led to rates far below national averages, researchers say. They also credit the long-acting highly effective methods of contraception chosen by 75% of the participants â?? namely intrauterine devices (IUDs) and hormonal implants.

The findings come as cost-free birth control is becoming available to more women under a much-debated provision of the federal health care law. The provision was supported by many women's health advocates but strongly opposed by the Catholic Church and many social conservatives. Dozens of lawsuits have been filed around the country. The study also comes weeks after the American College of Obstetricians and Gynecologists declared IUDs and implants front-line contraceptive choices for sexually active teen girls.

The study, published online in Obstetrics & Gynecology, was carried out in the St. Louis area from 2007 to 2011 and included participants ages 14 to 45 who said they wanted to avoid pregnancy for at least a year.

All were told about various methods of birth control and allowed to choose among them â?? but they did get counseling that stressed that IUDs and implants are much more effective than birth control pills and other methods, says lead researcher Jeffrey Peipert, professor of obstetrics and gynecology at Washington University School of Medicine.

Data suggest IUDs and implants fail up to 20 times less often than pills, which failed at a rate of about 4.5% in this study. Yet just 8.5% of U.S. women used IUDs and implants in 2009, says Megan Kavanaugh, senior research associate at the Guttmacher Institute in New York.

So the St. Louis researchers were stunned when 58% of the participants chose IUDs and 17% chose implants, Peipert says: "We found that when cost is not an issue, what is really important to women is that a method work really well."

Among the results:

-- A teen birth rate of 6.3 per 1,000 in the study, compared with 34.3 per 1,000 nationwide.

-- Annual abortion rates ranging from 4.4 to 7.5 per 1,000 women in the study vs. 13.4 to 17 per 1,000 in the region and to 19.6 per 1,000 nationwide in 2008, the most recent national data available.

-- Falling rates of repeat abortions in the entire St. Louis region but not nearby Kansas City. The researchers say this is linked to their study, which recruited some women from abortion clinics.

"These findings really show promise for what could happen on a national level," with a combination of free birth control and promotion of the most effective methods, Kavanaugh says.

Jeanne Monahan of the conservative Family Research Council suggested contraceptive use can encourage riskier sexual behavior. "One might conclude that the Obama administration's contraception mandate may ultimately cause more unplanned pregnancies since it mandates that all health plans cover contraceptives, including those that the study's authors claim are less effective," Monahan said.

The devices and insertion can cost several hundred dollars. An IUD, which contains copper or a progestin hormone, is inserted in the uterus and lasts five to 10 years. Hormone implants, the size of a matchstick, are placed in the arm and last three years.

Cost is not the only barrier to more widespread use, says Tina Raine-Bennett, research director at the Women's Health Research Institute at Kaiser Permanente Northern California. Many doctors don't suggest the long-acting methods, she says, because they are not trained to insert them or remember outdated information about a faulty IUD discontinued decades ago.

Raine-Bennett led the committee of obstetricians and gynecologists that recently recommended IUDs and implants for teens. "They are as effective as sterilization, but they are reversible," she says.

Under provisions of the Affordable Care Act that went into effect in August, insurers must cover birth control as well as many other preventive health services for women. Colleges, non-profits and other employers affiliated with religious organizations that object to the rule have been given an extra year to comply. A number of legal challenges by states and employers are underway; one was dismissed this week.